The present invention relates to a vehicle door handle circuit included in a vehicle door handle, configured for coupling to a vehicle-sided control device, the vehicle door handle circuit comprising an antenna circuit for emitting a signal to be sent, a control circuit and at least one actuation sensor, the control circuit being coupled to the actuation sensor for detecting an actuation, the antenna circuit comprising a series resonant circuit having a resonant circuit inductance and a resonant circuit capacitance, the vehicle door handle circuit having two contacts for coupling to the vehicle-sided control device via only two connection cables, via which the vehicle door handle circuit can receive a direct current supply voltage for supplying the control circuit or an alternating current voltage signal for driving the antenna circuit from the vehicle-sided control device, the antenna circuit being coupled between the two contacts, and the control circuit comprising two voltage supply junctions coupled to the two contacts.
The control circuit of the vehicle door handle circuit conventionally includes a microcontroller, which evaluates the signals of the actuation sensor for detecting an actuation of the vehicle door handle. The actuation sensor to which the control circuit is coupled, for example, can be a push button or a capacitive sensor. The transmitting antenna circuit in the vehicle door handle usually is driven by an alternating-current voltage to emit electromagnetic signals in the range of low frequency, for example, in a frequency range around 130 kHz.
The vehicle door handle by its first and second contact is coupled to the vehicle-sided control device only via two connection lines. The contacts can be formed by clamping, plug contacts or other contacting possibilities. Via these two connection cables, both the control circuit is supplied with voltage and the antenna circuit is driven to emit LF signals. Moreover, sensor signals are also transmitted to the control device via these two connection cables.
Numerous configurations of vehicle door handles, which feature sensor devices and also low frequency transmitting antennas, are known from the prior art.
One configuration according to the preamble of the present application can be concluded from the document JP 5589869 B2 as well as also from the document JP 5589870 B2.
These publications describe a door handle for use with so-called smart key systems or also smart entry systems. For this purpose, a user of a vehicle carries a wireless, portable device as a vehicle key. The device can be used for wirelessly locking or unlocking the door of a vehicle. Via the low-frequency antennas situated at the vehicle in the door handles, a vehicle-sided system emits signals, which are received by the portable device of the user. The portable device itself sends back information in the high-frequency range to the vehicle for identifying the portable device. There, this information is received by a suitable receiving arrangement (which is not located in the door handle), whereupon the identification is checked.
Both, the antenna for emitting the low-frequency signals and the means for detecting the actuation of the door handle are accommodated in the vehicle door handle. Regularly, the actuation by the hand of a user is detected in the door handle by sensor devices, for example capacitive proximity sensors or micro switches.
These devices in the vehicle door handle are coupled via a cable connector to a vehicle-sided control device. As disclosed by the aforementioned publications JP 5589869 B2 and JP 5589870 B2, the prior art mostly has featured configurations, in which the various lines, on the one hand, have been used for feeding and driving the low-frequency antenna and, on the other hand, for supplying the control circuit for detecting the actuation. In the document JP 5589870 B2, FIG. 6 shows such a system having a plurality of lines. For simplification purposes, the JP 5589870 B2 proposes to implement the driving and feeding of the antenna as well as of the control circuit via a shared line pair. For this purpose, FIG. 2 in JP 5589870 B2 shows a corresponding circuit, which here is reproduced in a simplified manner in FIG. 1. The line from the control device to the vehicle door handle is temporarily applied with a direct-current voltage to feed the control circuit and is temporarily applied with an alternating-current voltage, in particular a square-wave voltage, to drive the transmitting antenna.
For this purpose, the resonant circuit for the antenna circuit is situated in such a manner that, when applying a direct current voltage to the line, the antenna circuit blocks by its resonant circuit (the impedance becomes very large) and, for this reason, the direct current voltage is available at the control circuit. On the other hand, if an alternating current voltage is applied for exciting the resonant circuit, the antenna circuit sends the corresponding electromagnetic signals and its impedance becomes very small. In order to continuously supply the control circuit with voltage during this time, it is proposed in the prior art to tap off the voltage overshoot in the control circuit between capacitor and coil and to feed the voltage overshoot via a buffer capacitor into the control circuit.
It is the object of the invention to provide an alternative circuit arrangement for the described purpose.